Apparatus for manufacturing attenuator plugs



1 VENTQR. Kale/'2 R. GRIEGER Filed Feb. 1'7, 1966 'fiE/l' ATTORNEYS Jul 1, 1969 l I a wwi 3,452,395 APPPARATUS FOR MANUFACTURING ATTENUATOR PLUGS Robert Grieger, San Jose, Calif. (7 Fleet St., Marina Del Rey, Calif. 90291) Filed Feb. 17, 1966, Ser. No. 528,185 Int. Cl. B29c 13/00, 15/00 US. Cl. 18-16.5 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to an apparatus for molding attenuator plugs to the uninsulated sections of lead-in wires of electro-explosive devices such as initiators, detonators, actuators and squibs.

Attenuator plugs are attached to the lead-in wires of electro-explosive devices in order to prevent their premature ignition. The attentuator plugs attenuate high frequency energy which may be unintentionally induced into the wires. The lead-in wires act like antennas picking up these stray signals which induce a high frequency current into the wires causing the devices to explode or causing deterioration of the explosive charge so that it will not explode when given the correct signal. By providing an attenuator which is similar to a low pass filter across the lead-in wires, any high frequency current therein induced is efiectively short circuited out before it can set off or deteriorate the charge in the electro-explosive device. These attenuators, however, should not dissipate the actual ignition current which is passed over the wires from a blasting machine when it is desired to explode the device.

While it is to be understood that this invention is applicable to attenuators for any type of electro-explosive device, for purposes of explaining this invention such electro-explosive devices will be hereinafter referred to as detonators.

The attenuators are essentially a plug of compressed metal powder usually cylindrical in shape that has been formed about the uninsulated portions of the lead-in wires. A prior art method of manufacture of these plugs is to form them between two punches in a die which are forced together transverse to the longitudinal direction of the wires to compress the powdered metal about the wires. Since a feather edge can not be used on the edges of the punches, a long rectangular fiat running along the length of the plug must be left on the plug at the parting line 01 adjoining edges of the punches. These attenuators are relatively small and normally have a diameter of about a quarter of an inch and it is therefore difficult to remove these flats since the plugs are too small to fit into centerless grinding machines or other conventional smoothing apparatus.

Another method of manufacture is to make the plug in two halves and then to cement the two together about the wires.

The present invention provides an apparatus for forming the attenuators about wires of any length by compressing powdered metal around them in such a way that avoids the formation of any flats, leaving a smooth or uninterrupted outer surface on the attenuators.

ited States Patent Accordingly it is an object of this invention to provide an apparatus for the manufacture of attenuator plugs.

A further purpose of this invention is to provide an apparatus for compressing metal powder to form an attenuator plug'about electrical wires of indefinite length to avoid the necessity of subsequently joining the remainder of the lead-in wire to the attenuated portion of the wire.

A further purpose of this invention is to provide an apparatus for making attenuators that avoids the formation of flats on the plugs at the joints of the mold.

A further purpose of this invention is to provide an apparatus for axially compressing the powdered metal between two punches in an apertured die about the lead-in wires of a detonator.

A further purpose of this invention is to provide a lower punch member for the die constructed in separable parts to facilitate removal of the plug from the die after molding, but so designed that the parts are held together by the pressure exerted upon it during compression.

These and other objects will become more apparent from the following description of the drawings wherein like numbers designate like parts.

FIGURE 1 is a perspective of an electrical detonator lead-in wire having an attenuator attached thereto by the apparatus of this invention.

FIGURE 2 is a cross sectional view of the die assembly showing the relationship of one half of the separable lower punch member and the upper punch member with respect to the die.

FIGURE 3 is a fragmentary sectional view showing the die assembled for the formation of an attenuator.

FIGURE 4 is a sectional view of the separable lower punch member taken along the lines 4-4 of FIGURE 2.

FIGURE 5 is a vertical plan view of the lower punch member separated for insertion of the lead-in wires.

FIGURE 6 is a top plan view of the lower punch as shown in FIGURE 5.

With reference to the drawings, and particularly with reference to FIGURE 1, there is shown the uninsulated portions of lead Wires 10 and 11 for an electric detonator 12. Within the detonator there is an explosive charge which is ignited by a bridge wire 13 connected across the two ends of the lead wires within the detonator. The flow of current through the wire heats the bridge wire 13 which ignities the explosive within the detonator 12.

To prevent the premature firing of the detonators or degradation of the explosive charge by high frequency currents induced by various means into the lead wires, a protecting device 14 is attached across them which attenuates or reduces the current wave by short-circuiting the current across itself like low pass filter. These attenuators or attenuator plugs are preferably composed of a compressible powdered metal of ferrite or an insulated carbonyl iron powder as is well known to those skilled in the art.

In the embodiment of the invention as shown in FIG- URE 2, the die assembly consists of a die block 15 having a cylindrical shaped cavity 16 running through the center of the block. This cavity may be of any shape depending upon the shape of the attenuator desired but a cylindrical shape is preferred. At one end of the die the cavity tapers outwardly providing a machine chamfered surface 17. Adapted to mate within this end of the die, is a separable lower punch member 18 that comprises two halves 19 and 20 held in the proper position by two guide pins 21 suitably secured to the half 19 and slidably mounted into apertures 22 and 23 in the half 20. On the adjoining edges of the two halves are relatively large depressions 24 forming an annular chamber large enough to accommodate the insulation 24' on the lead wires when the punch is as- 3 sembled. The separable lower punch member when assembled is of less diameter than the diameter of the die block for ease in supporting the die block against relative movement when the lower punch is ejected from the die after formation of the plug as described below.

The separable lower punch includes a protrusion 25 comprising a cylindrical portion 26 carrying punch surface 27 adapted to fit in to the cavity 16 of the die block and also includes tapered portion 28 adapted to seat on the chamfered surface 17 of the die block. The angle of this chamfer is approximately 30. There are two relatively smaller depressions 30 on the adjoining edges of the protrusion of the two halves of the separable punch extending from the large depression 24 to the punch surface 27. Upon assembly of the lower puch, these small depressions form two separate chambers for positioning the exposed or uninsulated portions of the lead wires, 10 and 11. The lead wires extend for an indefinite length out of the lower punch opposite from the end carrying the protrusion 25 and out of the annular chamber 24.

A hollow upper punch member 31 is inserted into the opposite or top end of the cavity 16 of the die block. The upper punch includes a pressure surface 32 having two small apertures 33 therein adapted to receive the uninsulated portions of the lead-in wires positioned by the separable punch member 18.

In the operation of the die, the portions of the wires that have had their insulation removed are placed in the small depressions between the two halves of the separable lower punch which is then closed around the wires to position them with the remainder of the uninsulated portions of the wires extending upwardly as shown in FIGURE 3 from the end of the separable lower punch. The assembled lower punch is then inserted into the chamfered end of the die caivty so that the tapered portion 28 of the separable lower punch 18 seats against the cha-mfer 17 of the die block 15. The punch seats on thechamfer before the flat surface 29 of the punch 18 reaches the end of the die block 15. The lower punch surface 27 of the punch 18 is now located within the cavity 16.

A quantity of powdered metal 14 depending upon the size of the attenuator desired and composed of materials as described above is then poured into the upper end of the cavity of the die block.

The uninsulated portions of the lead wires, 10 and 11, should be at least long enough to extend completely through the cavity of the die block and out of the other end where they can easily be threaded into the appropriate holes 33 of the upper punch 31. The upper punch is then inserted into the cavity 16 with the pressure surface 32 leading and then depressed toward the punch surface 27 at the opposite end of the die, the upper punch 31 sliding with respect to the wires that are threaded therethrough.

While maintaining the die block and the separable lower punch in a fixed position, pressure is applied to the upper punch 31 by a hydraulic press or other suitable means until a predetermined amount of pressure between the two surfaces 27 and 32 has been reached, thereby compressing the powdered metal about the wires into a unitary structure. The pressure is then held for a specified length of time depending upon the type of metal used to achieve the proper consistency as is well known to those skilled in the art.

As the upper punch compresses the metal powder downwardly, the wires are carried along with it and hence they slide downwardly through the chambers 30 of the lower punch as the plug is being molded. These chambers 30 are only meant to hold the wires in proper position andnot to secure them against relative movement.

The tapered or chamfered portions 28 of the separable lower punch aid in centering the same within the die block, but principally are provided to keep the two halves of the lower punch together as pressure is applied against it by the die block 15. By providing a taper, the resultant force exerted M the lower punch by the die block acting against the taper 28, will resolve itself into a radial component F as shown in FIGURE 3 which will tend to push the halves together in addition to an axial component F tending to push the punch away from the die. Without this taper, the whole force component would be axial and this would 'allow the metal powder to force itself into the interface between the two halves of the separable punch tending to separate them.

While the die block and lower punch member are secured against relative movement during the molding operation, the frictional force created between the metal powder being compressed downwardly by the upper punch and the side walls of the cavity, forces the die downwardly against the lower punch. Since this pressure is applied against the tapered portion of the punch, the radial component of the resultant force will tend to press the two halves together.

While the taper 28 represents a preferred embodiment, it would be possible to eliminate the taper if other adequate means were provided for keeping the two halves together such as an annular ring member around the halves or a locking mechanism between them, but the taper provides the same without the necessity of utilizing additional elements.

Upon formation of the attenuator about the wires, the pressure on the upper punch is relieved and the separable lower punch member is released. The die block is now supported independently of the lower punch which is driven out of the die by the reapplication of pressure to the upper punch. When the lower punch is free of the die, it is then separated and removed from about the wires. Continued pressure by the upper punch will drive the attenuator plug with the wires attached thereto out the wide mouthed end of the die block. Upon removal of the upper punch, cleaning of the die block and lubrication of the elements, the die is ready for use for the manufacture of another attenuator plug.

The molding can either be carried out by hand in a laboratory manner, with suitable hand operated hydraulic press or else in a manufacturing process wherein the die block would be fixtured into an automatic hydraulic press. A production procedure would be similar to the procedure described above except that a feeding and clamping means for feeding the wires into the separable lower punch and holding them within this punch would have to be provided. In addition an upper clamping means would be needed to aid in the threading of the wires into the upper punch member.

In molding long plugs, several successive filling and pressing steps would be carried out by raising and lowering the upper punch with respect to the die block, adding more metal powder each time, without requiring removal of the lower punch.

Advantages in molding attenuator plugs in this manner are that the lead-in wires to which the plugs are molded can be of indefinite length and an intimate contact between the wires and the plug is achieved. Additionally the plugs are molded in one piece without any burrs or flanges thus eliminating post-forming steps formerly required such as removal of the flange or the cementing together of two halves of a plug. Thus continuous lead wires can be used from the electrical firing source to the electroexplosive device or detonator thereby eliminating any necessity of joining long lead-in wires to the short wires of a detonator having an attenuator attached thereto.

While the invention has been described with respect to molding an attenuator around two wires, it will readily be apparent that the invention is applicable to the molding of plugs about a single wire or any number of wires.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a device for molding a powdered metal attenuator plug about longitudinally extending electrical conductor wires of a detonator:

(a) a die having a continuous cavity extending longi- 5 6 tudinally therethrough, said cavity having a uniform die cavity, wherein said halves of said lower punch cross-section at its upper end and a tapering crossare restrained from parting radially by said tapering section at its lower end, cross-section of said die cavity. (b) an upper punch having a cross-section conforming to the cross-section of the upper end of the die 5 References Cited cavity and movable longitudinally within said upper end of the die cavity, the upper punch having holes UNITED STATES PATENTS for slidably receiving electrical conductor wires of 2. 2,289,787 7/1942 Kaschke et al 264111 dflonator, 3,274,318 9/1966 Spillane et a1. 264-111 (c) and a 9 Punch havmg f P 10 3,342,917 9/1967 Laskiewicz 264-109 cross-section to the lower end of the die cavity and longitudinally movable therein, said lower punch be- 3301111 2/1967 Braun 264 272 ing split longitudinally into two halves, each of the I I halves having parallel depressions therein for re- ROBERT WHITE P'lmmy Examine" ceiving the electrical conductor wires, each of said 15 J. R. HALL, Assistant Examiner.

halves being adaptable to move radially inward and close about said conductors and then move longitudinally upward into the die cavity to a position in 1g 3 29 203; 264 111 which said lower punch seats in the lower end of the 

